Flushing transmission fluid is good preventive maintenance on any vehicle, but is an especially important service on heavy trucks such as the Ford Explorer. Heavy vehicles (particularly those used for towing) place heavy loads on the the transmission fluid, causing it to degrade rapidly and wear out sooner. This procedure is simple, but can be risky, depending on the condition and age of your vehicle.

Word of Warning

Automotive transmission fluid changes drastically over time, and begins to infiltrate the clutches. After the infiltration of bad transmission fluid, your clutches will no longer grip the pressure plates if new fluid is introduced. Do not under any circumstances flush transmission fluid that smells burnt, is any color but red, or has been in the vehicle for more than 60,000 miles. Doing so will almost certainly result in fried clutches and a $1,500 repair bill.

Materials

You’re going to need two clean, empty milk jugs and about four feet of rubber fuel line. Purchase some 5/16-inch and some 3/8-inch hose lengths; different model years will require different sizes. You will need 16 quarts of transmission fluid. Buy two more quarts of fluid if you’re switching to a synthetic fluid. This would be a good time to consider changing your transmission’s filter; filter/gasket kits are available at your local auto parts store for about $15.

Preparation

Disconnect the rubber transmission cooler line connected to the radiator, just below the fill cap. Drop this hose into an empty plastic jug. Attach the appropriate-sized fuel line to the radiator nipple from which you disconnected the original hose, and secure it with a hose clamp. Drop the other end of that hose into the other milk jug.

Have an assistant start the truck briefly, and identify which hose is now spurting fluid. This is the fluid output line, and the non-spurting hose is the input line.

Flushing

If you’re changing your filter at this time, remove the transmission oil pan, replace the filter and refill your transmission as per the kit instructions.

Fill the input-line jug with fresh transmission fluid, and have an assistant start the truck. As the transmission sucks the fluid in, just keep the jug topped up with more. The empty jug will fill up with used fluid in about a 90 seconds. When it approaches the top, have your assistant shut the engine down while you dispose the used fluid into another container.

Repeat this procedure until all 16 quarts of new transmission fluid have been used, and the fluid coming from the output line is bright red. Reattach the transmission cooler line, start the truck and check for leaks.